The present invention relates to a joining head arrangement for joining components, such as studs, onto workpieces, such as metal sheets, comprising a housing and a slide that is mounted on the housing and is movable in a joining direction in relation to the housing by means of a linear drive, comprising at least one component holder, which is arranged on the slide and at which a component can be held during a joining operation, and comprising at least one feed device for feeding components, a component being transferred, at a transfer location, from the feed device to the component holder.
Further, the present invention relates to a method for feeding a component to a component holder and for joining the component onto a workpiece in a joining direction.
A joining head arrangement of the type described above is known, for example, from the document EP 1 495 828 B1.
In the present context, the term joining is intended to refer to all types of connection of elements, such as fastening elements, on workpieces, such as metal sheets, including adhesive bonding, forming, such as, for example, riveting, or combining of materials, such as, for example, welding. In particular, the term joining is intended here to relate to the joining of rotationally symmetrical components, such as studs, onto workpieces that are to be connected to the respective workpiece by, for example, short-time arc welding (stud welding) and/or by thermoplastic connection methods such as thermoplastic bonding or thermoplastic welding.
The components can be studs that have a shank and a head, or flange portion, having a somewhat greater diameter than the shank.
In the domain of stud welding, i.e. welding of metallic studs onto metal sheets, there is known the practice of feeding the studs to a joining head arrangement in an automated manner by means of a feed device.
In the case of the joining head arrangement known from the above-mentioned document EP 1 495 828 B1, the feeding of singled studs to the joining head arrangement is effected by compressed air. The stud holder is realized as a collet, which can be widened to a diameter of at least the flange diameter. The studs are fed into the holding device from behind, with the flange portion foremost, until the flange portion has emerged axially from the collet and the collet continues to hold only the shank of the stud. Starting from this position, a stud welding operation can then be performed, which operation can comprise, for example, the stages of placing the flange portion onto the workpiece, passing a pilot current through the stud and the workpiece, then raising the stud from the workpiece in order to draw an arc, switching over to a welding current, such that the mutually opposite surfaces of flange portion and workpiece become fused, and, finally, lowering the stud back onto the workpiece, until the arc is extinguished. At approximately the same time, the welding current is switched off, such that the combined melt solidifies and the stud is connected to the workpiece by material bonding.
Problematic in the case of the above joining head arrangement is that the component holder is subject to a large amount of wear. This is due to the elastic clamping elements of the component holder becoming overstretched by the relatively large cross-section of the flange portion.
A further joining head arrangement is known from the document DE 10 2005 044367 A1 (corresponds to publication US2007/0067975), which is under common ownership with this application and the disclosure of which is incorporated herein by reference. In the case of this arrangement, a housing, on which a slide is mounted in a linearly moveable manner, is rotatably mounted on an elongate arm. The feed device is fixed to the arm, and terminates in a transfer station. The housing can be so turned in relation to the arm that a stud, made available at the transfer station, is received there, in order subsequently to perform a joining operation with the received stud and following turning back to a joining position. In the case of this joining head arrangement, the cycle times are relatively long. In addition, the component holder is of relatively complex design, to enable the studs made available at the transfer station to be received in a reliable manner.